This is a tightly integrated, multidisciplinary effort involving fourteen investigators from seven divisions of the Washington University Medical Center. The three Core facilities, combined with the five Research Proposals, focus on normal relationships between brain and its vasculature, as well as the pathogenesis, diagnosis, and treatment of selected aspects of acute cerebrovascular disease. Evaluation of patients will involve the development and use of new tracer techniques involving the use of cyclotron-produced radiopharmaceuticals and positron emission tomography. In vivo tracer techniques will be used to examine exchange processes in the brain microvasculature as they might affect brain water content and, hence, volume. The role of platelets in cerebrovascular disease and platelet vessel interactions will be examined in vivo in man and an animal model using newly developed scanning techniques and radiolabeled platelets. The hemodynamic and metabolic criteria for and consequences of extracranial/intracranial arterial anastomosis will be examined using emission tomography and advanced tracer techniques. Finally, the role of vasospasm associated with subarachnoid hemorrhage will be studied in man using the same techniques.